In space applications, it is necessary to be able to orient certain elements, such as, for example, an antenna, a mast or an equipment item, of a satellite or of a spacecraft, in a predetermined direction in order, for example, to point them toward an external target such as a planet, a receiver, or a transmitter, to retain a pointing to a point on the surface of the Earth or even to scan a particular area on the surface of the Earth or of any celestial body. These positionings have to be frequently corrected, notably during target tracking phases, to compensate for inevitable drifts in maintaining this direction and these multiple corrections mean that a significant number of micro-rotation cycles have to be performed for these space appendages and for their guiding devices.
Given the irreversible nature of the act of placing a satellite in orbit, it is necessary to plane, when designing the spacecraft, a lifespan, measured as a number of cycles (one cycle corresponding to one rotational oscillation), that is very great for these guiding devices, so as to guarantee their capacity to withstand the very many stresses to which they are subject. For example, the desired lifespan may be greater than 300 000 cycles for tracking mechanisms. Other demands for the guiding devices are a strong mechanical performance capability notably with respect to the external forces and the bending moments exerted on the guided shaft, a high transversal rigidity, high precision guidance without play, a significant rotation amplitude for flexible elements, typically of the order of 5 to 10°, in both positive and negative directions, and a low and constant resisting torque.
The known guiding mechanisms are mounted on rolling bearing or other bearing types and require lubricants to ensure correct operation. These guiding mechanisms are not flexible and comprise a large number of parts which results in a reduced reliability compared to a flexible cardan joint. Furthermore, these non-flexible guiding elements are sensitive to the external loads and impacts during the launching of the spacecraft. Furthermore, they require a specific lubrication that is sensitive to the micro-displacements and to the extreme temperatures.
It is known practice to produce a flexible cardan joint consisting of four simple flexible pivots mounted in pairs in two different bearings, the four pivots defining two orthogonal rotation axes. The two bearings are linked together by a floating intermediate part and the two rotation axes are actuated by motor-drive mechanisms situated inside the two bearings. However, this cardan joint requires the use of two pivots for each rotation axis and an assembly of three different parts that are difficult to interleave with one another. Furthermore, this cardan joint has a significant bulk and a high weight due notably to the use of four different pivots and to bulky annular structures linking these different elements together. This cardan joint is therefore not applicable to the fine pointing of small appendages.